Sub-
Prefix meaning meaning under, below, less than normal, secondary, less than fully.
As in subacute, subaortic stenosis, subarachnoid, subclavian, subclinical disease, subcutaneous, subdural, subglottis, subjacent, sublingual, subluxation, and subtotal hysterectomy.
From the Latin preposition sub meaning under.
See also: Hypo-.